This invention relates to an article having permanent indicia thereon and to the use of such articles for marking electrical equipment, such as housings, wires and cables. In a preferred embodiment, the article is in the form of a heat stable marker suitable for use in marking cable.
Substrates such as wires, cables, equipment housing and the like are sometimes labeled with marker assemblies comprising a polymeric article marked with indicia, such as letters, numbers, or combinations thereof. To identify large diameter cables, electrical equipment or the like, relatively flat polymeric articles, frequently referred to as cable markers and panel markers, may be used. To identify individual wires, a marker assembly may comprise a sleeve, preferably heat recoverable, of a polymeric material such as a polyolefin, e.g. polyethylene, polyvinyl chloride, nylon or polyvinylidene fluoride. The indicia are generally typed or printed onto the article using a typewriter or computer printer. For many uses, the indicia need to be permanent (i.e. durable), e.g. resistant to smearing, to being rubbed off (i.e. abrasion resistant) and resistant to solvents which may contact the marker, as discussed more fully below. This latter requirement is generally specified for aircraft cable, which may come into contact with hydraulic fluid, liquid fuel, deicing solvents or the like. The mark is generally rendered permanent by a heat treatment. This heat treatment, referred to as "permatization", may take place by placing the sleeve in an oven, subjecting it to infrared radiation or, in the case of heat-recoverable sleeves, by the heat applied during the heat-recovery step. See for example U.S. Pat. No. 3,894,731 to Evans where infrared radiation is used to "permatize" the mark and U.K. Patent Application No. 2,181,142 where the mark is rendered permanent by application of heat during a heat shrinking step. An alternate technique of permanently marking wires, cables or the like is the relatively expensive "hot stamping" technique which requires special, expensive equipment to mark the wire or cable with heated foil.
Approaches for the production of articles with permanent indicia or marks without the need for "permatization" by heat treatment are disclosed in commonly assigned copending applications Ser. Nos. 017,520 and 171,589, filed Feb. 24, 1987 and Mar. 22, 1988, respectively, the entire disclosures of which are incorporated by reference. The former application describes a multilayer article comprising a first substantially nonporous polymeric layer bonded to a second porous absorbent, polymeric layer. The porous layer is capable of being marked with indicia which are resistant to organic solvents, smearing or abrasion. The multilayer article is relatively complicated to manufacture. One method of manufacturing the article is to bond a first layer of polymeric material to a second layer of polymeric material containing a leachable particulate material and then leaching the particulate material from the second layer to render it porous. The latter application describes an article in which the surface has a specified roughness found to be essential for obtaining permanent indicia without the need to heat treat or "permatize". Articles of the same composition but without the specified surface roughness could not be marked with permanent indicia without a "permatizing" treatment.
We have now discovered that an article having a surface made of a polymeric composition containing specified additives, as defined more fully below, is capable of receiving permanent indicia, i.e. indicia resistant to organic solvents, smearing and abrasion, without the need for a "permatizing" treatment.